Heterogeneity of somatostatin-like peptides in rat brain, pancreas, and gastrointestinal tract.

Somatostatin-like immunoactivities (SLI) in rat brain, pancreas, and gut were compared by gel filtration. Three species of SLI could be identified in most tissues after acid extraction. The apparent molecular weight of the largest detectable species of SLI ranged from 12,000 (K) daltons in rat brain to 17K daltons in pancreas and gut. A second, intermediate sized SLI (approximately 4K daltons) was detected in all extracts, but this 4K species was particularly abundant in intestinal mucosa. A third, small form of SLI was also found in all tissues which contained SLI. This form coeluted with synthetic somatostatin and represented the largest percentage of total SLI in most tissues. The relationship between the various SLI peptides is uncertain. In terms of molecular size and anatomic distribution, rat 4K SLI is reminiscent of somatostatin-28, which has been isolated from porcine intestine.